title: Ratiometric fluorescent sensor based on inhibition of resonance for detection of cadmium in aqueous solution and living cells.
abstract: Although cadmium has been recognized as a highly toxic heavy metal and poses many detrimental effects on human health, the Cd(2+)-uptake and nosogenesis mechanisms are still insufficiently understood, mainly because of the lack of facile analytical methods for monitoring changes in the environmental and intracellular Cd(2+) concentrations with high spatial and temporal reliability. To this end, we present the design, synthesis, and photophysical properties of a cadmium sensor, DQCd1 based on the fluorophore 4-isobutoxy-6-(dimethylamino)-8-methoxyquinaldine (model compound 1). Preliminary investigations indicate that 1 could be protonated under neutral media and yield a resonance process over the quinoline fluorophore. Upon excitation at 405 nm, 1 shows a strong fluorescence emission at 554 nm with a quantum yield of 0.17. Similarly, DQCd1 bears properties comparable to its precursor. It exhibits fluorescence emission at 558 nm (Φ(f) = 0.15) originating from the monocationic species under physiological conditions. Coordination with Cd(2+) causes quenching of the emission at 558 nm and simultaneously yields a significant hypsochromic shift of the emission maximum to 495 nm (Φ(f) = 0.11) due to inhibition of the resonance process. Thus, a single-excitation, dual-emission ratiometric measurement with a large blue shift in emission (Δλ = 63 nm) and remarkable changes in the ratio (F(495 nm)/F(558 nm)) of the emission intensity (R/R(0) up to 15-fold) is established. Moreover, the sensor DQCd1 exhibits very high sensitivity for Cd(2+) (K(d) = 41 pM) and excellent selectivity response for Cd(2+) over other heavy- and transition-metal ions and Na(+), K(+), Mg(2+), and Ca(2+) at the millimolar level. Therefore, DQCd1 can act as a ratiometric fluorescent sensor for Cd(2+) through inhibition of the resonance process. Confocal microscopy and cytotoxicity experiments indicate that DQCd1 is cell-permeable and noncytotoxic under our experimental conditions. It can indeed visualize the changes of intracellular Cd(2+) in living cells using dual-emission ratiometry.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Lin
authors.initials: L
authors.lastname: Xue
authors.forename: Guoping
authors.initials: G
authors.lastname: Li
authors.forename: Qing
authors.initials: Q
authors.lastname: Liu
authors.forename: Huanhuan
authors.initials: H
authors.lastname: Wang
authors.forename: Chun
authors.initials: C
authors.lastname: Liu
authors.forename: Xunlei
authors.initials: X
authors.lastname: Ding
authors.forename: Shenggui
authors.initials: S
authors.lastname: He
authors.forename: Hua
authors.initials: H
authors.lastname: Jiang
mesh_terms: D000818:Animals; D002104:Cadmium / Q000032:analysis*; D002470:Cell Survival; D018360:Crystallography, X-Ray; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry*; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D015394:Molecular Structure; D041681:NIH 3T3 Cells; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D012996:Solutions; D014867:Water / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D009942:Organometallic Compounds; D012996:Solutions; D002104:Cadmium; D014867:Water